cc3265 at albnyvms.bitnet wrote:
: An interesting theory was put forth by a linguist named MacNeilage --
: concerning tree-dwellers & handedness. In this uniquely challenging
: environment manual specialization may have occurred -- each hand skilled
: for certain things -- because of the dangers involved in having to decide
: each time what hand to use. The left hand actually was the more specialized
: at first, it was used anytime quick movement (called ballastic movement) was
: required -- like catching bugs, for example. The right hand was utilized for
: hanging onto the tree, and so, eventually, became stronger, specialized for
: activities requiring strength & fine-motor control. Observations of tree-
: dwelling primates today seems to lend some support to this theory.
I think MacNeilage is the first to come up with an explanation showing
adaptive value for asymmetry in any plausibly prelinguistic behaviour;
this is a big step forward.
Most other theories about brain asymmetry for language either
concern themselves with whether it's one way rather than the other,
ignoring why there should be any asymmetry at all. A few point out
that the high-speed, precise articulatory constraints of speech can be
satisfied more easily by short, intrahemispheric connections than
they can by the longer, and correspondingly slower, interhemispheric
connections that would be necessary for symmetrical neurolinguistic
processing. But this only predicts asymmetry, not consistently
left-sided asymmetry.
A properly satisfying explanation of neurolinguistic asymmetry would:
1. deal with human language in a framework that makes contact with
similar communicative and noncommunicative behaviors in all primates
(including H.sapiens), and with weaker correlation, more distantly
related species.
2. explain the inheritance of the asymmetry by recognizing that
genes (DNA sequences) specify protein enzymes, not behavior. To
get from genes to behavior you have to go through a reasoning
process like this: DNA in the egg's nucleus is translated into
regulatory enzymes that shape the pathways by which dividing
cells become neurons with particular classes of connections.
Only when those connections start operating do you get behavior
that you can see.
3. explain why the asymmetry is to the left rather than the right.
Since language BEHAVIOR is symmetrical, the direction of the neural
asymmetry must be a historical accident, a "symmetry-breaking" event.
All you can ask about such an event is "when did it occur?"
MacNeilage's theory says it occurred when our ancestors went
into the trees. You can also suggest that asymmetry was there all
along and was simply released when the need to use all four limbs
for locomotion was dropped. Asymmetry is present in the layout
of most of the internal organs in vertebrates, why not the brain?
Asking whether asymmetrical brain activity is involved in language,
and how it works, is one question. Asking why this asymmetry
exists, how it got to be that way, is a different kind of question,
requiring you to think in a biological context, not a medical one.
And "nothing in biology makes sense except in the light of evolution."
Including relative clauses and pronouns.
- George McKee
--
Internet: mckee at neosoft.com
Voice: +1 713 890 8122
